Method and apparatus for reducing packet retransmission during handover (ho) in low latency mobile networks

ABSTRACT

Interruptions in communication due to user equipment (UE) handovers (HO) are signaled from the mobile communication network to the traffic source. For ultra-low latency and reliable communication, the signaling of HO start and completion notifications prevents retransmissions of in-flight packets by the traffic source, eliminating additional delays and inefficiencies. Signaling can be implemented by a network element, by a network element in conjunction with a smart traffic handler between the network and the traffic source (e.g., applications) and by a UE having at least two different radio interfaces.

TECHNICAL FIELD

The embodiments of the invention relate to wireless communications and,more particularly, to a system and method for supporting ultra-lowlatency and reliable communication by preventing retransmissions ofin-flight packets by a traffic source during a handover (HO) of userequipment (UE) from one base station to another.

BACKGROUND

As technology advances, new products and services are created that havenew communication requirements in terms of throughput, signal qualityand transmission delay. Many of these new use cases such as augmentedreality/virtual reality (AR/VR), gaming, self-driving cars, remotemedical imaging, etc., require low latency and reliability. For example,some transmissions require about a 1 millisecond end-to-end latencyand/or lossless transmissions such that retransmissions occur if packetsare lost. Most of these use cases utilize Transmission Control Protocol(TCP), where the end-to-end transport control keeps track of whichpackets are acknowledged and which packets require retransmission. If anacknowledgement signal (ACK) is not received within a timeout period fora packet, then the packet is retransmitted.

A new user plane for a future generation network (e.g., 5G) hasend-to-end latency that is significantly less than HO duration and asmall retransmission timeout period. As a result, traffic sources aremore likely to retransmit packets already buffered in the network due tothe mobility management mechanism, thereby causing excessive duplicationin high data rate communications and more latency.

Problems that occur when HO duration (T_(h)) is significantly greaterthan round trip time (RTT), that is, the duration for a small InternetProtocol (IP) packet to travel from a traffic source through the networkto a destination, and back, will now be illustrated with reference toFIG. 1. FIG. 1 depicts a mobile communication network 16 wherein a UE 22undergoes a HO from a first base station (e.g., a source E-UTRAN NodeB(SeNB)) 14 a to a second base station (e.g., target eNB (TeNB)) 14 b. Inhigh-speed networks, a traffic source 20 sends a relatively large numberof packets. The traffic source sets a retransmission timeout period asα×RTT (where α>1, but small). The traffic source is self-clocked by ACKsfrom the UE 22. In other words, the traffic source 20 sends more packetsas more ACKs are received from the UE 22. Once a packet's retransmissiontimeout period expires, the subsequent in-flight packets also expire andare retransmitted and clocked by the ACK of earlier packets. During HO,in-flight packets are buffered in the network 16 and the UE 22 is in anoutage state (e.g., the UE 22 cannot transmit or receive any packets).Since HO time is much greater than end-to-end retransmission timeout,all in-flight packets before the handover (i.e., P₁ to P_(K)) expire andare retransmitted by the traffic source 20, which creates congestion andmore latency after HO is completed.

SUMMARY

In accordance with aspects of an illustrative embodiment, a method isprovided for reducing retransmission between a traffic source and a userequipment (UE) during UE handover (HO) in a mobile communicationnetwork, comprising: upon detection of UE HO, generating andtransmitting to the traffic source a HO start notification to indicatethat an outage time window is beginning; determining that UE HO issubstantially complete or is complete; and generating and transmittingto the traffic source a HO completion notification to indicate that theoutage time window is closed. For example, generating and transmittingthe HO start notification and the HO completion notification isperformed by a mobile communication network component. For example, themobile communication network component is selected from a groupconsisting of a network exposure function component (NEF) when thenetwork is a 5G network and a service capability exposure functioncomponent (SCEF) when the network is a 4G network.

In accordance with aspects of an illustrative embodiment, the mobilecommunication network component is a NEF, the traffic source is at leastone internet protocol (IP)-based application running on an applicationserver, and the generating and transmitting a HO start notificationfurther comprises the steps of: querying, by the NEF, a user planefunction component (UPF) to receive application flow informationassociated with the UE; and generating and transmitting, by the NEF, aHO start notification to each application associated with the UE basedon the application flow information. The HO start notification indicatesto the application that packet traffic transmitted from the applicationto the UE is temporarily interrupted during HO and to stop sendingpacket traffic to the UE.

In accordance with aspects of an illustrative embodiment, the generatingand transmitting a HO completion notification further comprisesgenerating and transmitting, by the NEF, a HO completion notification toeach application associated with the UE based on the application flowinformation. The HO completion notification indicates to the applicationthat packet traffic transmitted from the application to the UE isresuming following HO and to resume sending packet traffic to the UE.

In accordance with aspects of an illustrative embodiment, the mobilecommunication network component is a NEF, the traffic source is at leastone internet protocol (IP)-based application running on an applicationserver, and a smart traffic handler is provided between the network andthe at least one application and operates as a Transmission ControlProtocol (TCP) split proxy. Generating and transmitting the HO startnotification further comprises generating and transmitting, by the NEF,a HO start notification to the smart traffic handler, and generating andtransmitting the HO completion notification further comprises generatingand transmitting, by the NEF, a HO completion notification to the smarttraffic handler.

In accordance with aspects of an illustrative embodiment, generating andtransmitting the HO start notification and the HO completionnotification is performed by a UE. For example, the UE receives a HOstart signal via a first radio interface. The UE has a second radiointerface and a processor programmed to implement a transport controlfor communicating with at least one application server by the secondradio interface and having running application information. Generatingand transmitting the HO start notification to the traffic sourcecomprises: providing the HO start signal to the transport control; andthe transport control sending the HO start notification with a UE IPaddress via the second radio interface to the at least one applicationserver based on the running application information, the HO startnotification indicating the beginning of the outage time window for thefirst radio interface.

In accordance with aspects of an illustrative embodiment, in response tothe UE receiving HO completion signal the first radio interface, thegenerating and transmitting to the traffic source the HO completionnotification comprises: providing the HO completion signal to thetransport control, and the transport control sending the HO completionnotification via the second radio interface to the at least oneapplication server, the HO completion notification indicating theclosing of the outage time window for the first radio interface. The atleast one application server pauses transmission of traffic to the UEvia the first radio interface in response to the HO start notification,and resumes the transmission of traffic to the UE via the first radiointerface in response to the HO completion notification.

In accordance with aspects of an illustrative embodiment, a networkexposure function component (NEF) in a mobile communication networkcomprises: an Internet Protocol (IP) interface to an IP network; anetwork function (NF) message interface to other components of themobile communication network, the NEF receiving user equipment (UE)handover (HO) start signals and HO completion signals from at least oneof the other components of the mobile communication network via thenetwork function message interface; a memory storage comprisinginstructions for communicating with applications running on at least oneapplication server in the IP network, and for generating HO startnotifications and HO completion notifications; and a processor incommunication with the IP interface, the NF message interface and thememory storage, wherein the processor executes the instructions togenerate and transmit a HO start notification to at least one of theapplications via the IP interface after receiving a HO start signal viathe NF message interface, and to generate and transmit a HO completionnotification to the at least one of the applications via the IPinterface after receiving a HO completion signal via the NF messageinterface, the HO start notification indicating that an outage timewindow is beginning, and the HO completion notification indicating thatthe outage time window is closed. For example, the processor executesthe instructions to query a user plane function component (UPF) toreceive application flow information associated with the UE comprisingthe applications to which the UE is subscribed and for which a sessionwith UE is established during HO, and to generate and transmit the HOstart notification and the HO completion notification to eachapplication associated with the UE based on the application flowinformation.

In accordance with aspects of an illustrative embodiment, a smarttraffic handler component (STH) comprises: an Internet Protocol (IP)interface to at least one application server in an IP network and to amobile communication network component having an IP network interface; amemory storage comprising instructions for implementing at least one ofa Transmission Control Protocol (TCP) split proxy and a User DatagramProtocol (UDP) packet handler, and for processing a HO startnotification and a HO completion notification received from the mobilecommunication network component via the IP interface; and a processor incommunication with the IP interface and the memory storage, wherein theprocessor executes the instructions to pause a TCP packet retransmissiontimer and begin an outage time window via the TCP split proxy inresponse to the HO start notification and then resume the TCP packetretransmission timer and close the outage time window in response the HOcompletion notification. Further, the processor executes theinstructions to buffer packets directed to the UE from the applicationserver, stop sending the packets to the UE from the application serverin response to the HO start notification, and resume sending packets tothe UE from the application server in response to the HO completionnotification, via the UDP packet handler.

In accordance with aspects of an illustrative embodiment, a UserEquipment (UE) in a mobile communication network comprises: a firstradio interface connecting the UE to the mobile communication network; asecond radio interface connecting the UE to an Internet Protocol (IP)network; a memory storage comprising one or more applications running onthe UE and instructions for implementing a transport control forcommunication between the applications and their correspondingapplication servers in the IP network, the transport control comprisingrunning application information indicating the applications to which theUE is subscribed and with which the UE is having a session; and aprocessor in communication with the IP interface and the memory storage,wherein the processor executes the instructions to provide a handover(HO) signal received via the first radio interface to the transportcontrol, to send via the transport control a HO start notification witha UE IP address via the second radio interface to at least one of theapplication servers based on the running application information, the HOstart notification indicating the beginning of the outage time windowfor the connection established over the first radio interface. Forexample, in response to the UE receiving a HO completion signal via thefirst radio interface, the processor executes the instructions to sendvia the transport control a HO completion notification via the secondradio interface to the application server, the HO completionnotification indicating the closing of the outage time window for thefirst radio interface.

Additional and/or other aspects and advantages of the present inventionwill be set forth in the description that follows, or will be apparentfrom the description, or may be learned by practice of the invention.The present invention may comprise software, APIs, non-transitory memorywith instructions, network elements, UEs and application servers andmethods for operating same having one or more of the above aspects,and/or one or more of the features and combinations thereof. The presentinvention may comprise one or more of the features and/or combinationsof the above aspects as recited, for example, in the attached claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or other aspects and advantages of embodiments of theinvention will be more readily appreciated from the following detaileddescription, taken in conjunction with the accompanying drawings, ofwhich:

FIG. 1 illustrates a UE undergoing HO in a mobile communication networkand packet retransmission.

FIG. 2 is a diagram depicting a system wherein mobile communicationnetwork components provide HO notifications to traffic sources such asapplications to reduce packet retransmissions during HO in accordancewith an illustrative embodiment.

FIG. 3 illustrates signal flow of components in the system of FIG. 2.

FIGS. 4A and 4B are flow charts depicting operations by a mobilecommunication network component and a traffic source, respectively, forreducing packet retransmission during HO in a mobile communicationnetwork in accordance with an illustrated embodiment.

FIG. 5 is a block diagram of a network exposure function component (NEF)in accordance with an illustrative embodiment.

FIG. 6 is a diagram depicting system wherein mobile communicationnetwork components are configured to provide HO notifications to a smarttraffic handler component (STH) in accordance with an illustrativeembodiment.

FIG. 7 illustrates signal flow of components in the system of FIG. 5.

FIG. 8 is a block diagram of a STH in accordance with an illustrativeembodiment.

FIG. 9 is a diagram depicting a system wherein a user equipment (UE) isconfigured to provide HO notifications to traffic sources such asapplications in accordance with an illustrative embodiment.

FIG. 10 illustrates signal flow of components in the system of FIG. 9.

FIGS. 11A and 11B are flow charts depicting operations by a UE and atraffic source, respectively, for reducing packet retransmission duringHO in a mobile communication network in accordance with an illustrativeembodiment.

Throughout the drawing figures, like reference numbers will beunderstood to refer to like elements, features and structures.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In accordance with an advantageous aspect of embodiments of theinvention, signaling (e.g., from the mobile communication network to atraffic source) of interruptions in communication due to UE HOs is usedto prevent retransmissions of in-flight packets by the traffic source,thereby eliminating additional delays and inefficiencies to supportultra-low latency and reliable communication. As described below,illustrative embodiments send HO start and completion notifications to atraffic source. A traffic source is, for example, an application (App)in an operator domain or third party application, or a proxy, etc., thatsends packets to a UE. The traffic source can then pause aretransmission timer to open an outage time window to avoid packetretransmission during HO, optionally stop sending traffic to a UE whenthat UE is in HO mode, and then resume the retransmission timer to closethe outage time window when HO is completed.

The illustrative embodiments are implemented using either one of twotechniques for reducing retransmissions. For the first technique, acomponent in the network 16 sends the traffic source 20 two signals,that is, a first signal hereinafter referred to as a “HO startnotification” to indicate the start of a HO, and a second signalhereinafter referred to as a “HO completion notification” to indicatethe completion of the HO. The traffic source 20, in turn, pauses itsretransmission timer after receiving the HO start notification to beginan outage time window during which no packets are retransmitted to theUE, and resumes the retransmission timer after receiving the HOcompletion notification to close the outage time window and resumeretransmission of packets. The traffic source 20 can optionally stopsending new packets between receiving the HO start notification and thenreceiving the HO completion notification. For the second technique, a UE22 is attached to multiple radio interfaces (e.g., a mobilecommunication network interface and a WiFi interface), and the HO startnotification and the HO completion notification are sent to the trafficsource 20 by the UE 22 rather than a network 16 component.

FIGS. 2 and 3 illustrate an embodiment using the first technique wherebya network component 32 in a mobile communication network 16 sends HOstart notifications and the HO completion notifications to a trafficsource 20. FIG. 2 illustrates various components in a mobilecommunication network 16 and in an IP network 26, and FIG. 3 depictssignal flow between the components. The network 16 is shown as a fifthgeneration (5G) mobile communication network; however, it is understoodthat the network 16 can be a third Generation (3G) Partnership Projectstandard (3GPP) network or a fourth generation (4G) Long Term Evolution(LTE) mobile communication network, for example. Traffic sources such asIP network-based Apps 20 send packets to a UE 22 via a user planefunction (UPF) 34. A UE 22 undergoes HO from a SeNB 14 a to a TeNB 14 b.For HO in a 4G LTE network, a mobility management entity (MME) receivesa HO request signal from a SeNB and commands handover, and receivesnotification from a TeNB when HO is complete. Similar signals areprovided from a SeNB and a TeNB to a session management function (SMF)30 in a 5G network. The SMF 30 communicates HO start and completionsignals to a network component 32 such as a service capability exposurefunction (SCEF) in a 4G network or a network exposure function (NEF) ina 5G network which, in turn, provide HO start and completionnotifications to traffic sources 20. As illustrated by the lines labeled“I” through “6” in FIGS. 2 and 3, the following actions 1 through 6occur in accordance with the illustrated embodiment:

1. When the SMF 30 receives a signal indicating the beginning of HO fromthe SeNB 14 a, the SMF 30 sends the NEF 32 a signal with UE identity(e.g., international mobile subscriber identity (IMSI)) that isindicated as “HO Start” in FIG. 3.

2. Upon receiving the HO start signal from the SMF 30, the NEF 32queries the UPF 34 to get flow information associated with the UE 22.The flow information pertains to those applications 20 to which the UE22 is subscribed and for which a session is currently established withthe UE 22. As described below in accordance with an aspect of theillustrated embodiment, Apps 20 are configured to receive HO startnotifications and HO completion notifications when the UE is subscribedto the Apps and engaged in existing sessions with them during HO. TheUPF 34 receives flow information from the Apps pertaining to the networkidentifiers of subscribed UE in existing sessions with the Apps. In someinstances, an App 20 may only be able to provide the UPF 34 with its endpoint information (e.g, server IP address and port number of App server24 for the App 20) when a UE network identifier of a subscribed UEengaged in a session with the App is hidden (e.g., when the UE is behinda network address translator (NAT)). In these instances, the end pointsprovided to the UPF 34 that have subscription context for the UE aresent HO start notifications and HO completion notifications.

3. The UPF 34 responds to the NEF 32 with the flow information relatingto the UE 22.

4. The NEF 32 sends HO start notifications to the relevant Apps 20 thatsend traffic to the UE 22 (e.g., based on the flow information acquiredin step 3). Each of the Apps 20 stops sending packets to the UE 22. Forexample, upon receiving a HO start notification, the App 20 begins anoutage time window by pausing a retransmission timer via its applicationserver 24. The outage time window is later closed by resuming theretransmission timer upon receiving a HO completion notification.

5. The NEF 32 receives from the SMF 30 a signal with the UE's IMSI andindicating that HO is almost complete. The signal from the SMF 30 isindicated as “HO Complete” in FIG. 3.

6. The NEF 32 sends HO completion notifications to the relevant Apps 20based on the flow information. Each of the Apps 20 resumes sendingpackets to the UE 22, and closes the outage time window by resuming theretransmission timer upon receiving the HO completion notification.

As stated above, the mobile communication network 16 can be a 3GPP or 4GLTE network, or other mobile communication network besides a 5G network,wherein a MME, SCEF and a serving/packet data network gateway (S/P GW)are used, for example, in place of the SMF, NEF and UPF described inconnection with FIG. 2. The explicit HO start notifications and HOcompletion notifications provided to the traffic sources 20 from thenetwork 16 as described herein and in accordance with illustrativeembodiments can be implemented using different mobile communicationnetwork components in different types of communication networks.Regardless of the type of network 16, a network component such as an MMEin a 4G network or a SMF 30 detects HO start as indicated in block 50 ofFIG. 4A, and then a HO start notification is transmitted to the trafficsource(s) 20 (e.g., Apps), as indicated in block 52, such as by an SCEFin a 4G network or a NEF 32. As indicated by arrows (ii) in FIG. 4A, analternative signaling sequence can be used whereby the network 16 doesnot have to wait for the completion of HO start notification to thetraffic source(s) to commence UE HO procedure. The network 16 commencesthe UE HO procedure (block 54) and, once completion of HO is detected(block 56) by the MME or SMF 30, a HO completion notification isgenerated and transmitted to the traffic source(s) (block 58) by theSCEF or NEF 32. On the traffic source side (FIG. 4B), a traffic sourcereceives the HO start notification (block 60), and then pauses aretransmission timer (block 62), and optionally stops sending newpackets (block 64). When the traffic source receives the HO completionnotification (block 66), the traffic source resumes the retransmissiontimer (block 68) and, if the sending of packets was paused, then thetraffic source resumes sending new packets (block 70).

It is understood that a Protocol Independent Network Condition Service(PINCS) can provide the HO start signals and the HO completion signalsto the NEF 32 instead of an SMF 30. A PINCS, for example, can be part ofa network congestion controller that also comprises a network conditionconsumer (NCC) node and a network condition provider (NCP) node. ThePINCS is operable to aggregate information about network conditions andsend the aggregated information to NCC node as indicated by thesubscription. The NCP applies the subscribed network conditioninformation to a congestion control algorithm to implement congestioncontrol on the network. A PINCS is described in U.S. patent applicationSer. No. 15/796,183, filed Oct. 27, 2017, which is incorporated hereinby reference in its entirety. The SMF 30, UPF 34 and NEF 32 depicted inFIG. 2 can be implemented, for example, as a network element on adedicated hardware, or a software instance running on a dedicatedhardware, or as a virtualized function instantiated on an appropriateplatform such as a cloud infrastructure.

FIG. 5 depicts an example NEF 32 for transmitting HO start notificationsand HO completion notifications to a traffic source(s) 20. The NEF 32comprises a network function (NF) message interface 86 for communicatingwith other mobile core entities such as with the SMF 30 to receivesignals indicating HO start and HO completion and with the UPF 34 toobtain UE flow information. The NEF 32 further comprises an IP interface84 for communicating with entities in an IP network 26 such asapplication servers 24 and Apps 20. The NEF 32 can have a processor 80configured to implement software instructions stored in memory 82 tocontrol its operations. For example, the instructions can be a set ofapplication programming interfaces (APIs) at the network 16 boundary tothe IP network 26 for communicating with Apps 20 running on at least oneapplication server 24 in the IP network 26 to send HO startnotifications and HO completion notifications based on flow informationobtained from the UPF 34 and in response to HO start signals and HOcompletion signals, respectively, received from the SMF 30.

FIGS. 6 and 7 illustrate another embodiment using the first techniquewhereby a network component 32 in a mobile communication network 16sends HO start notifications and the HO completion notifications to asmart traffic handing component (STH) 36 in the IP network 26 instead ofthe traffic source 20 as described in FIGS. 2 and 3. FIGS. 6 and 7 aresimilar to FIGS. 2 and 3, respectively, except for the addition of theSTH 36. The STH 36 is an interface between the mobile communicationnetwork 16 and applications 20 accessible via app server(s) 24 in the IPnetwork 26 and can operate as a TCP split proxy and a User DatagramProtocol (UDP) packet handler. For example, when the SMF 30 receives asignal indicating commencement of HO for a UE 22, the following actions1 through 6 occur:

1. When the SMF 30 receives a signal indicating the beginning of HO fromthe SeNB 14 a, the SMF 30 sends a HO start signal with UE identity(IMSI), or UE IP address if IP address is statically allocated, to theNEF 32.

2. Upon receiving the HO start signal, the NEF 32 uses the IMSI to querythe UPF 34 to get the UE IP address. On the other hand, if thenotification includes the UE IP address, this action is obviated.

3. The UPF 34 responds to the NEF 32 with the UE IP address if queried.

4. The NEF 32 sends a HO start notification with UE IP address to theSTH 36. When the HO start notification is received, the STH 36 controlsa TCP packet retransmission timer for its TCP split proxy function toavoid packet retransmission during HO. The TCP split proxy of the STH 36interacts with applications 20 as if nothing occurs. In other words, HOstart or completion notifications are not sent to the applications 20,and the applications do not pause transmission of packets or pauseretransmission timers. Instead, the TCP split proxy of the STH 36 beginsan outage time window (e.g., by pausing the TCP retransmission timer),stops sending packets towards the UE 22, and buffers those packets. TheSTH 36 also buffers UDP packets going to the UE 22 using the UDP packethandler.

5. When the SMF 30 receives a signal indicating that HO is almost done,the SMF 30 sends a HO completion signal to the NEF 32.

6. The NEF 32 notifies the STH 36 about the UE 22's HO completion, andthe TCP split proxy of the STH 36 closes the outage time window (e.g.,by resuming the TCP packet retransmission timer), and starts sendingpackets to the UE22. For UDP packets, STH 36 simply forwards the packetsto the UE 22.

FIG. 8 depicts an example STH 36 configured for receiving HO startnotifications and HO completion notifications from an NEF 32 andcommunicating with traffic source(s) 20. The STH can be dedicatedhardware, or a virtualized function instantiated on an appropriateplatform such as a cloud infrastructure. The STH 36 comprises, forexample, an IP interface 98 for communicating with the NEF 32 andentities in the IP network 26 such as application servers 24 and Apps20. Further, the STH 36 can have a processor 90 configured to implementsoftware instructions stored in memory 92 to control its operations suchas its TCP split proxy operations 94 and UDP packet handler operations96.

With continued reference to FIGS. 6 and 7, it is understood that a PINCScan provide the HO start and HO completion signals to the NEF instead ofan SMF, as stated above in connection with FIGS. 2 and 3. Further, in a3GPP or 4G LTE network, or other mobile communication network besides a5G network, a MME, SCEF and S/P GW are used in place of the SMF/PINCS,NEF and UPF described in connection with FIGS. 2 and 3 in accordancewith an illustrative embodiment. The explicit HO start and completionnotifications to the STH described herein and in accordance withillustrative embodiments can be implemented using different mobilecommunication network components in different types of communicationsnetworks.

FIGS. 9 and 10 depict another illustrative embodiment employing thesecond technique wherein a UE 22 sends notifications to the trafficsource 20 regarding HO status. The second technique employs dualconnectivity where a UE is attached to multiple radio interfaces (e.g.,a mobile communication network interface and a WiFi interface), andutilizes a transport layer that delivers over these multiple radiointerfaces. In FIGS. 9 and 10, a UE 22 undergoes HO in a mobilecommunication network 16 between SeNB 14 a and TeNB 14 b. The UE 22 hasat least two different radio interfaces RIF-1 38 ₁ and RIF-2 38 ₂ suchas a mobile communication network interface and a WiFi interface,respectively. Other combinations of radio interfaces can be used. The UE22 communicates with traffic sources such as IP network-basedapplications 20 available via app server(s) 24. For example, thefollowing actions 1 through 4 occur:

1. When a UE 22 learns about a HO start signal from an SeNB 14 a via theRIF-L 38 ₁ (step 100 in FIG. 11A), the HO start signal is passed totransport control 100, which has the running applications' informationas indicated at 42 (step 102 in FIG. 11A).

2. The transport control 100 sends HO start notifications with UE IPaddress to the app servers 24 running on the IP network 26 via the RIF-238 ₂, as indicated at step 104 in FIG. 11A When the app servers 24receive the HO start notifications (step 110 in FIG. 11B), the appservers 24 begin an outage time window to avoid retransmission ofpackets during HO (e.g., by pausing a retransmission timer), andoptionally stop sending traffic to the UE via its network 16 interfaceRIF-1 38 ₁, as indicated in step 112 of FIG. 11B.

3. When the UE 22 learns that HO is complete from the TeNB 14 b via theRIF-1 38 ₁ (step 106 of FIG. 11A), a HO complete signal is passed to thetransport control 100.

4. The transport control 100 at the UE 22 sends HO completenotifications to the app server(s) 24 via the RIF-2 38 ₂ (step 108 ofFIG. 11A). When the app server(s) 24 receive the HO completionnotifications (step 114 in FIG. 11B), the app servers 24 resume theretransmission timer to close the outage time window and resume sendingtraffic to the UE 22 via its network 16 interface RIF-1 38 ₁, ifpreviously paused, as indicated in step 116 of FIG. 11B

Illustrative embodiments advantageously enable explicit signaling ofinterruptions in communication due to UE handovers from the network 16or UE 22 to the traffic source(s) 20. For ultra-low latency and reliablecommunication, this signaling prevents retransmissions of in-flightpackets by the traffic source, thereby eliminating additional delays andinefficiencies.

The HO start and completion notifications of the illustrativeembodiments are implemented, for example, by a set of APIs for a mobilecore network which provide improved support for low latency applicationsand allow for a more efficient transmission pipeline by preventingduplicate transmissions of packets. Illustrative embodiments can also beimplemented as edge transport proxy services or functions.

Illustrative embodiments of the present invention are useful in anevent-driven environment where the transport control at an applicationor network entity can wait for HO start and completion notifications. Inaccordance with an aspect of the illustrative embodiments, the messagesand interfaces for HO start and completion notifications exchangedbetween the mobile core platform and the transport control layers can bestandardized for compatibility and use by different core networks and UEsuch as Internet Engineering Task Force (IETF) Transport LayerExtensions (e.g., QUIC, BBR, TCP, MP-TCP, and the like), and OpenNetworking Foundation (ONF) Software-Defined Networking (SDN) APIs.

Accordingly, illustrative embodiments advantageously provide simplermobility management solutions that offload packet buffering to thetransport control layer, as well as provide a solution to an emergingproblem that is inadequately addressed by existing solutions. Forexample, no solution exists in the area of mobile communication networksto address HO time being significantly greater than round trip time andtherefore presenting a new problem. Existing solutions are generallyoutside 3GPP Mobility Management, and mainly adapt against end pointnetwork identifier changes, rely on end-to-end signals, and cannothandle outages. These existing solutions are not aware of changes in HOstate or outages due to HO but rather only rely on historical dataregarding transmissions. These existing solutions merely maketransmission scheduling decisions based on the historical data andsignal quality capability, neither of which are known at the applicationlayer or TCP layer of the Internet Protocol suite. By contrast,illustrative embodiments of the present invention advantageously exposeHO events, allowing HO information to be provided for schedulingdecisions.

It will be understood by one skilled in the art that this disclosure isnot limited in its application to the details of construction and thearrangement of components set forth in the following description orillustrated in the drawings. The embodiments herein are capable of otherembodiments, and capable of being practiced or carried out in variousways. Also, it will be understood that the phraseology and terminologyused herein is for the purpose of description and should not be regardedas limiting. The use of “including,” “comprising,” or “having” andvariations thereof herein is meant to encompass the items listedthereafter and equivalents thereof as well as additional items. Unlesslimited otherwise, the terms “connected,” “coupled,” and “mounted,” andvariations thereof herein are used broadly and encompass direct andindirect connections, couplings, and mountings. In addition, the terms“connected” and “coupled” and variations thereof are not restricted tophysical or mechanical connections or couplings. Further, terms such asup, down, bottom, and top are relative, and are employed to aidillustration, but are not limiting.

The components of the illustrative devices, systems and methods employedin accordance with the illustrated embodiments of the present inventioncan be implemented, at least in part, in digital electronic circuitry,analog electronic circuitry, or in computer hardware, firmware,software, or in combinations of them. These components can beimplemented, for example, as a computer program product such as acomputer program, program code or computer instructions tangiblyembodied in an information carrier, or in a machine-readable storagedevice, for execution by, or to control the operation of, dataprocessing apparatus such as a programmable processor, a computer, ormultiple computers.

A computer program can be written in any form of programming language,including compiled or interpreted languages, and it can be deployed inany form, including as a stand-alone program or as a module, component,subroutine, or other unit suitable for use in a computing environment. Acomputer program can be deployed to be executed on one computer or onmultiple computers at one site or distributed across multiple sites andinterconnected by a communication network. Also, functional programs,codes, and code segments for accomplishing the present invention can beeasily construed as within the scope of the invention by programmersskilled in the art to which the present invention pertains. Method stepsassociated with the illustrative embodiments of the present inventioncan be performed by one or more programmable processors executing acomputer program, code or instructions to perform functions (e.g., byoperating on input data and/or generating an output). Method steps canalso be performed by, and apparatus of the invention can be implementedas, special purpose logic circuitry, e.g., an FPGA (field programmablegate array) or an ASIC (application-specific integrated circuit), forexample.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an ASIC, a FPGA or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read-only memory ora random access memory or both. The essential elements of a computer area processor for executing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,magnetic, magneto-optical disks, or optical disks. Information carrierssuitable for embodying computer program instructions and data includeall forms of non-volatile memory, including by way of example,semiconductor memory devices, e.g., electrically programmable read-onlymemory or ROM (EPROM), electrically erasable programmable ROM (EEPROM),flash memory devices, and data storage disks (e.g., magnetic disks,internal hard disks, or removable disks, magneto-optical disks, andCD-ROM and DVD-ROM disks). The processor and the memory can besupplemented by, or incorporated in special purpose logic circuitry.

Those of skill in the art understand that information and signals may berepresented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill in the art further appreciate that the variousillustrative logical blocks, modules, circuits, and algorithm stepsdescribed in connection with the embodiments disclosed herein may beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, circuits,and steps have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware orsoftware depends upon the particular application and design constraintsimposed on the overall system. Skilled artisans may implement thedescribed functionality in varying ways for each particular application,but such implementation decisions should not be interpreted as causing adeparture from the scope of the present invention. A software module mayreside in random access memory (RAM), flash memory, ROM, EPROM, EEPROM,registers, hard disk, a removable disk, a CD-ROM, or any other form ofstorage medium known in the art. An exemplary storage medium is coupledto the processor such the processor can read information from, and writeinformation to, the storage medium. In the alternative, the storagemedium may be integral to the processor. In other words, the processorand the storage medium may reside in an integrated circuit or beimplemented as discrete components.

Although the present disclosure has been described with reference tospecific features and embodiments thereof, it is evident that variousmodifications and combinations can be made thereto without departingfrom scope of the disclosure. The specification and drawings are,accordingly, to be regarded simply as an illustration of the disclosureas defined by the appended claims, and are contemplated to cover any andall modifications, variations, combinations or equivalents that fallwithin the scope of the present disclosure.

1. A method for reducing retransmission between a traffic source and auser equipment (UE) during UE handover (HO) in a mobile communicationnetwork, the method comprising: upon detection of UE HO, generating andtransmitting to the traffic source a HO start notification to indicatethat an outage time window is beginning; determining that UE HO issubstantially complete or is complete; and generating and transmittingto the traffic source a HO completion notification to indicate that theoutage time window is closed.
 2. The method of claim 1, whereingenerating and transmitting the HO start notification and the HOcompletion notification is performed by a mobile communication networkcomponent.
 3. The method of claim 2, wherein the mobile communicationnetwork component is selected from a group consisting of a networkexposure function component (NEF) when the network is a 5G network and aservice capability exposure function component (SCEF) when the networkis a 4G network.
 4. The method of claim 3, wherein the mobilecommunication network component is a NEF, the traffic source is at leastone internet protocol (IP)-based application running on an applicationserver, and the generating and transmitting a HO start notificationfurther comprises the steps of: querying, by the NEF, a user planefunction component (UPF) to receive application flow informationassociated with the UE; and generating and transmitting, by the NEF, aHO start notification to each application associated with the UE basedon the application flow information.
 5. The method of claim 4, whereinthe generating and transmitting a HO completion notification furthercomprises generating and transmitting, by the NEF, a HO completionnotification to each application associated with the UE based on theapplication flow information.
 6. The method of claim 4, wherein the NEFis notified of detection of UE HO by another mobile communicationnetwork component selected from a group consisting of a sessionmanagement function component (SMF) and a protocol independent networkcondition service component (PINCS) that send a HO start signal with UEInternational Mobile Subscriber Identity) IMSI to the NEF, and thedetermining status of completion of UE HO comprises the other mobilecommunication network component sending the NEF a HO completion signalwith UE IMSI.
 7. The method of claim 3, wherein the mobile communicationnetwork component is a NEF, the traffic source is at least one internetprotocol (IP)-based application running on an application server, and asmart traffic handler is provided between the network and the at leastone application and operates as a Transmission Control Protocol (TCP)split proxy, the generating and transmitting the HO start notificationfurther comprising generating and transmitting, by the NEF, a HO startnotification to the smart traffic handler, and the generating andtransmitting the HO completion notification further comprisinggenerating and transmitting, by the NEF, a HO completion notification tothe smart traffic handler.
 8. The method of claim 7, wherein the NEF isnotified of detection of UE HO by another mobile communication networkcomponent selected from a group consisting of a SMF and a PINCS thatsends a HO start notification with at least one of UE IMS1 and UE IPaddress to the NEF.
 9. The method of claim 8, further comprisingquerying, by the NEF, a UPF to receive a UE IP address if not receivedfrom the SPF or the PINCs.
 10. The method of claim 1, wherein generatingand transmitting the HO start notification and the HO completionnotification is performed by a UE.
 11. The method of claim 10, whereinthe UE receives a HO start signal via a first radio interface and the UEhas a second radio interface and a processor programmed to implement atransport control for communicating with at least one application serverand having running application information, and the generating andtransmitting to the traffic source the HO start notification comprises:providing the HO start signal to the transport control; and thetransport control sending the HO start notification with a UE IP addressvia the second radio interface to the at least one application serverbased on the running application information, the HO start notificationindicating the beginning of the outage time window for the first radiointerface.
 12. The method of claim 10, wherein, in response to the UEreceiving a HO completion signal via the first radio interface, thegenerating and transmitting to the traffic source the HO completionnotification comprises: providing the HO completion signal to thetransport control; and the transport control sending the HO completionnotification via the second radio interface to the at least oneapplication server, the HO completion notification indicating theclosing of the outage time window for the first radio interface.
 13. Anetwork exposure function component (NEF) in a mobile communicationnetwork comprising: an Internet Protocol (IP) interface to an IPnetwork; a network function (NF) message interface to other componentsof the mobile communication network, the NEF receiving user equipment(UE) handover (HO) start signals and HO completion signals from at leastone of the other components of the mobile communication network via thenetwork function message interface; a memory storage comprisinginstructions for communicating with applications running on at least oneapplication server in the IP network, and for generating HO startnotifications and HO completion notifications; and a processor incommunication with the IP interface, the NF message interface and thememory storage, wherein the processor executes the instructions togenerate and transmit a HO start notification to at least one of theapplications via the IP interface after receiving a HO start signal viathe NF message interface, and to generate and transmit a HO completionnotification to the at least one of the applications via the IPinterface after receiving a HO completion signal via the NF messageinterface, the HO start notification indicating that an outage timewindow is beginning, and the HO completion notification indicating thatthe outage time window is closed.
 14. The NEF of claim 13, wherein theprocessor executes the instructions to query a user plane functioncomponent (UPF) to receive application flow information associated withthe UE comprising the applications to which the UE is subscribed and forwhich a session with UE is established during HO, and to generate andtransmit the HO start notification and the HO completion notification toeach application associated with the UE based on the application flowinformation.
 15. A smart traffic handler component (STH) comprising: anInternet Protocol (IP) interface to at least one application server inan IP network and to a mobile communication network component having anIP network interface; a memory storage comprising instructions forimplementing at least one of a Transmission Control Protocol (TCP) splitproxy and a User Datagram Protocol (UDP) packet handler, and forprocessing a HO start notification and a HO completion notificationreceived from the mobile communication network component via the IPinterface; and a processor in communication with the IP interface andthe memory storage, wherein the processor executes the instructions topause a TCP packet retransmission timer and begin an outage time windowvia the TCP split proxy in response to the HO start notification andthen resume the TCP packet retransmission timer and close the outagetime window in response the HO completion notification.
 16. The STH ofclaim 15, wherein the processor executes the instructions to bufferpackets directed to the UE from the application server, stop sending thepackets to the UE from the application server in response to the HOstart notification, and resume sending packets to the UE from theapplication server in response to the HO completion notification, viathe UDP packet handler.
 17. A User Equipment (UE) in a mobilecommunication network comprising: a first radio interface connecting theUE to the mobile communication network; a second radio interfaceconnecting the UE to an Internet Protocol (IP) network; a memory storagecomprising one or more applications running on the UE and instructionsfor implementing a transport control for communication between theapplications and their corresponding application servers in the IPnetwork, the transport control comprising running applicationinformation indicating the applications to which the UE is subscribedand with which the UE is having a session; and a processor incommunication with the IP interface and the memory storage, wherein theprocessor executes the instructions to provide a handover (HO) startsignal received via the first radio interface to the transport control,to send via the transport control a HO start notification with a UE IPaddress via the second radio interface to at least one of theapplication servers based on the running application information, the HOstart notification indicating the beginning of an outage time window forthe radio interface.
 18. The UE of claim 17, wherein, in response to theUE receiving a HO completion signal via the first radio interface, theprocessor executes the instructions to send via the the transportcontrol a HO completion notification via the second radio interface tothe application server, the HO completion notification indicating theclosing of the outage time window for the first radio interface.